The present invention relates to processing of line state signaling in communications networks, and particularly although not exclusively for processing of channel associated signaling in circuit switched networks such as Asynchronous Transfer Mode (ATM) networks.
Conventional telecommunication systems handling telephony and other circuit switched data calls comprise a plurality of central office exchange switches each communicating with each other to form a national and/or international network, each central office switch communicating with a large number of subscriber apparatus, for example, telephone handsets, fax machines, modems. In general each subscriber apparatus is connected to a local exchange over one or a plurality of line circuits. Each line circuit is bi-directional, having two channels. FIG. 1 herein illustrates schematically part of a conventional telecommunications network comprising a plurality of subscriber terminals 100-103, each subscriber terminal connected to a corresponding local exchange apparatus 104, 105, the local exchanges being interconnected as part of a larger network, for example an international network comprising a plurality of international exchanges 106, 107. Set up and termination of calls between individual user terminals is initiated by a sequence of signals passed between the subscriber terminals, the local exchanges and the international exchanges. Typically, such signaling comprises a number of different tone sequences, for example a call waiting indication tone; a recall dial tone; a message waiting tone; a confirmation tone, a ringing tone; a line busy tone; a reorder tone; a receiver off hook tone; and a continuity check tone. Analog tone levels at transmitting and receiving user terminals are defined in International Telecommunications Union (ITU) recommendations ITU Q.312 and ITU Q.213. For example, to set up a call, a user may pick up a telephone handset which results in an off hook line seizure signal which is converted into a digital bit stream, either at the telephone handset, or at the local exchange, and which is monitored by a call control processor at the local exchange. The off hook signal is followed by a plurality of dial tone signals representing telephone numbers, which are converted into a digital bit stream either at the subscriber terminal, or at the local exchange. The off hook signal is converted at the first local exchange into a digital bit stream and is then routed by the call control processor over the entire telecommunications network to a destination specified by the dial tones. For example in the case illustrated schematically in FIG. 1, the off hook signal generated by first user terminal 100 is received at first local exchange 104. After a predetermined number of digits have been dialed at first user terminal 100, local exchange 104 recognizes that a call has to be routed to first international exchange 106 and generates a seizing signal, comprising a pattern of bits which is communicated to first international exchange 106 by first local exchange 104. Similarly, first international exchange 106 on receiving the seizing condition signal from first local exchange 104 recognizes the seizing condition signal and generates a further seizing condition signal to second international exchange 107, and so on as the call propagates across the network and is routed to second local exchange 105 to which the destination of the call, ie, second user terminal 102, is connected. At each exchange, there is a delay in processing the signaling. The signals can only change every 1.5 to 2 ms. Further, the signals themselves have a duration, depending upon the type of signal. Each exchange monitors a plurality of line circuit channels, and on receiving a signal on a circuit will only recognize that signal after the signal has persisted for a predetermined duration. For example, where first user terminal 100 generates an off hook signal, first local exchange 104 monitoring a line to which the first user terminal is connected must determine that the off hook signal has persisted for a predetermined duration, before the first local exchange will recognize the signal as a valid off hook signal. Typically, such predetermined duration is of the order of 10 ms. Further, each intervening exchange, ie, first international exchange 106, second international exchange 107 and second local exchange 107 requires the off hook signal to persist for a minimum duration of 10 ms before the relevant exchange will recognize the off hook signal as being valid. At each exchange, changes in a line state must persist for a predetermined duration before the corresponding call control process of a local exchange recognizes that line change state as being valid. Thus, for a 14 digit dialed national telephone code, typically a maximum of the order of 8 to 10 exchanges would be involved. The delay at each exchange would comprise a 10 ms delay to confirm persistence of a line change state, plus a delay incurred by the local call control processor to process the line change state and signal to a next exchange. Over an extended telecommunications network, call set up may take of the order of 0.5 seconds in all. At each exchange, each line connected to that exchange is periodically polled by the call control processor, checking for changes in line state on each line repetitively every 1 or 2 ms. This places a data processing burden on the call control processors. The data processing requirement for checking each line at an exchange every 1 or 2 ms includes the processing overhead of polling the line, retrieving line state data from the line, comparing the received line state data with a previously received line state data from the same line and determining whether a change has occurred, and if a change is determined to have occurred on the line, performing additional signal processing to check whether that change in line state persists on that line, ie, counting the number of times which a line has been in a particular state. The call control processor carries out the polling procedures on an interrupt basis, interrupting its normal call control data processing operations to check each line individually. Thus, the call control processor is not doing useful call control processing operations during this time, but is performing data processing associated with persistence monitoring operations of line state.
For example, during an average 3 minute call, less than 30 seconds will be spent performing dialing and initial call set up. This requires generation of 5 message events thus, in a typically longest national dialed call there will be 14 digits dialed, giving 14 dialed digit events, plus an initial seizure event. Thus, when a subscriber goes off hook and dials a 14 digit number, assuming each individual line state is aggregated, then in one direction from the subscriber to the exchange, in 3 minutes there are 15 events transmitted on one line. If the signaling is being handled by the conventional call control processor which polls every 1.5 ms, there are of the order 660 polls per second, or about 39,000 polls per minute, so over the duration of the 3 minute call the processor may poll the line state over 100,000 times. Considering that each exchange may handle a large number of calls at any one time, the data processing burden on the call control processor due to the line state persistence measurement consumes a significant proportion of the data processing capacity of the processor.
Thus, as the number of lines which a single call control processor is required to service increases, the data processing burden due to the line state persistence measurement process increases for that processor, at the expense of using data processing capacity which could otherwise be used for call control data processing operations.
One object of the present invention is to provide a method and apparatus for devolving the processing of persistence measurements of line state from the handling of call control signaling, thereby improving the efficiency of call control processing and the efficiency of line state persistence measurement processing.
Another object of the present invention is to integrate a system for handling devolved line state persistence measurement and call control processing with an Asynchronous Transfer Mode transport system.
According to a first aspect of the present invention, there is provided a signal processing apparatus for processing channel associated signaling data, said processing apparatus comprising:
interface means for interfacing with a plurality of line circuits for receiving circuit signals on said plurality of line circuits;
signaling extraction means receiving circuit signals from said interface, said signal extraction means extracting said channel associated signaling data from said circuit signals;
frame assembly means, for assembling said extracted channel associated signaling data relating to said plurality of line circuits into a plurality of data frames; and
event message generation means operating to receive a plurality of said data frames, and to output an event message in response to a change of circuit status data contained within said data frames.
Said interface may comprise an interface for communicating etc, wherein said interface comprises an interface for communicating with a plurality of line circuits selected form the following set:
T1;
E1;
OC3;
STM 1.
Preferably, said event message generation means comprises:
data storage means for storing data describing a state of each of a plurality of said circuits;
means for comparing data signals contained in a currently received data frame, each said set of data signals relating to a current status of a said circuit;
means for comparing said stored status data with said currently received status data for each of said circuits; and
means for generating an event message, when a said change of state is detected.
Preferably said signal processing apparatus further comprises:
means for assembling an event message data frame in response to a detected change of state of at least one said circuit.
Preferably said signal processing apparatus further comprises means for storing said event message data frames and for regulating a flow of said event message data frames onto a communications back plane.
According to a second aspect of the present invention, there is provided a signal processing apparatus for processing channel associated signaling data, said processing apparatus comprising:
means for receiving at least one event message describing a change of state of at least one line circuit; and
means for generating a plurality of data frames, each said data frame comprising data describing a status of each of a plurality of said line circuits;
wherein a status data content of said data frames is changed in response to an event message contained within a said event message data frame.
The apparatus may further comprise a means for regulating a plurality of said output data frames for entry onto a communications back plane.
Said means for generating a plurality of said data frames preferably comprises;
a robbed bit signaling code generator means; and
means for generating a plurality of tone signals, said tone signals relating to a each of a plurality of said circuits.
Preferably said means for generating a plurality of said data frames operate to continuously generate said data frames.
Preferably said means for receiving at least one event message comprises a store for storing a plurality of transport carriers containing said event messages.
Preferably said means for receiving at least one event message comprises a message buffer.
According to third aspect of the present invention, there is provided a method for processing channel associated signaling data of a plurality of communications channels, said method comprising the steps of:
extracting channel associated signaling data from channel signaling carried on each of said plurality of communications channels;
assembling said extracted channel associated signaling data of said plurality of communication channels into at least one data frame;
monitoring a plurality of said data frames to detect changes of line status of said plurality of communications channels; and
generating an event message data frame in response to a said detected change of status.
Preferably said method further comprises the step of inserting a said event message data frame into transport carrier payload.
A said transport carrier payload may comprise a payload in accordance with a protocol selected from the set:
Asynchronous Transfer Mode (ATM);
Transmission Control Protocol (TCP);
Synchronous Digital Hierarchy (SDH).
Preferably a said event message data frame is inserted into an AAL 5 cell payload.
Said step of monitoring a plurality of said data frames may comprise:
sequentially inspecting each of a plurality of data locations within a said data frame, each said data location corresponding to an individual said communications channel line circuit; and
comparing a content of each said data location within said data frame with a corresponding data location stored in a data storage device, said corresponding stored data location containing stored data relating to a previous state of said corresponding communications channel.
Preferably said step of monitoring a plurality of said data frames comprises:
checking a persistence of a said change of status by counting a number of said data frames over which channel associated signaling describing said status persists.
Preferably said step of assembling said extracted channel associated signaling data into a least one data frame comprises assembling channel associated data of at least one trunk into a single said data frame.
Preferably said channel associated signaling data corresponds to a trunk selected from the set:
a T1 trunk;
an E1 trunk;
an OC3 trunk;
an STM 1 frame;
is assembled into a single said data frame.
A said data frame may comprise an AAL 0 48 byte payload.
Preferably said method comprises the step of outputting said event message data frames asynchronously in response to a said detected change of status.
According to a fourth aspect of the present invention there is provided a method of processing channel associated signalling data of a plurality of line circuits, said method comprising the steps of:
assembling channel associated signaling data describing a current status of each of a plurality of said line circuits into a first data frame;
for each said line circuit, storing historical status data in a memory area;
for each said line circuit, comparing said current status data contained in said first data frame with said historical stored data; and
if said current status data in said first data frame differs from said stored historical status data, assembling a second data frame type containing said current status data.
Said step of for each said line circuit comparing said current status data contained in said first data frame with said historical stored data may comprise:
monitoring each of a plurality of data locations in said first data frame, each said data location containing data describing a status of a corresponding said line circuit; and
comparing a content of said data location with a content of a corresponding stored data location in a data storage device.
A said first data frame may comprise an AAL 0 payload, or an AAL 5 payload.
A second said data frame may comprise an AAL 0 payload or an AAL 5 payload payload.
Preferably said step of assembling channel associated signaling data comprises packing said channel associated signaling data into said data frame according to a predetermined packing algorithm.
According to a fifth aspect of the present invention there is provided a method of processing channel associated signaling data of a plurality of line circuits, said method comprising the steps of:
receiving a first input data frame containing data describing a current status of a said line circuit;
storing historical line status data describing an historical status of said line circuit;
comparing said current status data of said line circuit with said historical status data of said line circuit;
receiving at least one further input data frame containing further data describing a current status of said line circuit;
checking that said further data received in said further data frame corresponds with said current data received in said first data frame; and
assembling said current data into at least one output data frame.
The invention includes a method of processing channel associated signalling data of a plurality of line circuits, said methods comprising the steps of:
assembling channel associated signaling data for each of a plurality of said line circuits into a data frame;
for each line circuit, storing historical status data in a memory area;
for each said circuit comparing said current status data contained in said data frame with said historical stored data;
if said current status in said data frame differs from said stored historical status data, assembling an event message data frame containing said current status data.
Specific embodiments according to the present invention may allow for a typical 3 minute call, a reduction from of the order of 100,000 interrupts to a call control processor to be replaced, in the case of, for example a 14 digit dialed call, by of the order of 15 signaling events.
The invention includes a signal processing apparatus for processing channel associated signaling data of a plurality of telecoms lines circuits, said processing apparatus comprising:
a plurality of interface means each interfacing with a plurality of line circuits for receiving circuit signals on said plurality of said line circuits;
a plurality of signal extraction means receiving said circuit signals from said plurality of interfaces, said signal extraction means extracting said channel associated signaling data from said plurality of circuit signals;
a plurality of frame assembly means, each for assembling said extracted channel associated signaling data relating to a corresponding respective plurality of respective line circuits into a plurality of data frames;
a plurality of event message generation means operating to receive a plurality of said data frames and to output an event message in response to a change of circuit status data contained within said data frames.
The invention includes a signal processing apparatus for processing channel associated signaling data, said processing apparatus comprising:
a plurality of means for receiving at least one event message describing a change of state of at least one line circuit; and
a plurality of means for generating a plurality of data frames, each said data frame comprising data describing a status of each of a plurality of said line circuits;
wherein a status data content of said data frames is changed in response to an event message contained within a said event message data frame.